The idea of the day, launched five years ago, is to promote the lifesaving potential of handwashing with soap as a worldwide habit.
It was created for children and schools - but, of course, anyone can participate.
It is the most effective and cheapest way to prevent serious problems like diarrhoea and respiratory infections, such as influenza and pneumonia, which claim the lives of millions of children in developing countries. They are responsible for most child deaths.
Since the handwashing day started, the number of children dying from diarrhoea each year has halved - that's 1.1 million lives saved. Yet 3,000 children under the age of five still die from diarrhoea every year.
This year was the first time the international campaign has been taken up in Hong Kong. Our junior reporters visited the Unicef office in Hong Kong to learn about the importance of washing your hands, and they also attended a soap-making workshop.
The importance of soap
Washing your hands with soap before meals and after going to the toilet is an everyday habit for most of us, although some people still fail to do so. They are spreading germs and disease.
However, for many people living in developing countries, it can be hard to find a supply of clean water and soap for washing.
Pneumonia and diarrhoea are two major killer diseases in countries with a lot of poor people.
However, if people wash their hands with soap, the rate of catching diarrhoea can be reduced by 45 per cent, and serious respiratory infections, such as pneumonia and influenza, by 23 per cent.
Even in Hong Kong, disadvantaged families overlook the importance of soap, and rarely put it on the shopping list.
After the workshop, participants were asked to donate their handmade soap to Unicef, which planned to distribute it to poor families in Hong Kong.
Soap may look tiny and insignificant, but when it's in the hands of the needy, it can make a real difference.
Six steps to washing your hands
Rinsing your hands with water alone is not enough to remove germs. You must use soap or sanitiser gel and follow these tips.
1. Put soap or sanitiser gel onto the palm of one hand. Rub palm to palm.
2. Then, scrub your palms against the backs of your hands; this way, most of the germs on the surface of your hands will be killed.
3. After that are the fingers. Put your palms back together, interlock your fingers and scrub them against one another.
4. Scrub the back and tips of your fingers against your palms.
5. Don't forget to clean your thumbs in the same way. These are the five important finger-washing steps.
6. Lastly, your wrists are also close to your hands, and could carry bacteria. So make sure you wash your wrists, too. You should wash your hands under running water, then rinse and dry throughly.
When we arrived, we found a bar of old-looking white, hotel soap, a grater, some food colouring, a few cookie cutters and a plastic bowl on a table.
First, we grated the bar of soap into very small granules. This part was difficult because it was tiring.
It's important to take care, too; failing to concentrate may result in a few cuts on your fingers.
After we had gathered enough granules, we added droplets of water so we could knead the granules into a dough. It's at this point that you add the colours.
Once the dough takes shape, stuff it in the cookie cutter to carve the shape you want. It's quite similar to making a ceramic.
However, of course, it smells much nicer, looks better and is more practical.
Young Post Junior Reporters' Club organises regular activities for our members. If you want to be part of it, send an e-mail with your name, age, school and contact telephone number to email@example.com, with "jun rep application" in the subject bar